President Trump on Monday slashed a pair of national monuments in Utah, marking an unprecedented rollback of his predecessors' legacies and prompting protests and threats of lawsuits from conservation groups as well as praise from Western conservatives.

During a speech in Salt Lake City, Trump proclaimed that "public lands will once again be for public use," saying that he would reduce the size of Bears Ears and Grand Staircase-Escalante national monuments, both in southern Utah.

“I’ve come to Utah to take a very historical action,” Trump said of his announcement, “to reverse federal overreach and resort the rights of this land to your citizens.”

Interior Secretary Ryan Zinke told reporters Monday morning that Bears Ears would go from about 1.3 million acres to 220,000 acres. Grand Staircase-Escalante would be reduced from 1.8 million acres to about 1 million acres. Previously leaked maps indicated the two monuments would also be broken into a total of five smaller preserves.

President Obama created Bears Ears National Monument in the final days of his presidency. It was the result of a years-long lobbying effort from a coalition of Native American tribes and conservation groups. The designation was vehemently opposed by Utah's congressional delegation, with multiple lawmakers vowing to work to undo the designation. Utah lawmakers also said they would attempt to modify the Antiquities Act, the 1906 law that allows presidents to create national monuments.

President Clinton created Grand Staircase-Escalante National Monument in 1996.

Trump announced the changes during his first visit as president to Utah. The visit was met with multiple days of protests, including gatherings Monday at the state capital and elsewhere in Salt Lake City.

Demonstrators in Salt Lake City displayed signs condemning the plan to shrink the monuments.

The protests highlight the intensity that surrounds the larger debate over how to treat public lands. In western states such as Utah, Nevada, and Idaho, the federal government owns the majority of the total land. Some of that land is used for popular national parks, such as Zion and Arches, as well as parklike monuments including Bears Ears and Grand Staircase-Escalante.

However, vast swaths of the public land in the west are not part of designated preserves and are available for activities such as grazing.

National monuments are a particular source of controversy because the Antiquities Act lets presidents create them without congressional approval. Resistance to monuments led Trump earlier this year to order Zinke to review all monuments created since 1996. The review wrapped up in August, and the announcement Monday in Utah was prompted by Zinke's recommendations.

During his speech Monday, Trump repeatedly characterized the creation past monuments as federal "overreach," and said past presidents had "abused the purpose, spirit, and intent" of the Antiquities Act. He also said that the "timeless bond" Utahns have with their land "shouldn’t be replaced by the whims of regulators."

"Our precious national treasures must be protected and they from now on will be protected," the president added.

But a host of Native American and environmental groups disputed that and condemned the announcement Monday. In a statement, Navajo Nation President Russell Begaye said that the decision to reduce Bears Ears "is being made with no tribal consultation."

"The Navajo Nation will defend Bears Ears," Begaye added. "The reduction in the size of the monument leaves us no choice but to litigate this decision."

The threat of lawsuits was a recurring theme Monday. Wilderness Society President Jamie Williams, for example, called the reductions "illegal" and an "insult to the owners of this land," adding that changes would be challenged in court.

Other groups that criticized Trump's announcement Monday include the Center for Biological Diversity, National Parks Conservation Association, the National Audubon Society, the Pew Charitable Trusts, Defenders of Wildlife, the Nevada Conservation League, the Center for Western Priorities, and others. Many of the groups opposing the reductions also promised to sue.

However, across the political aisle, Trump won praise Monday. Sen. Orrin Hatch, a Utah Republican, introduced Trump Monday and described the long process of working to undo the Bears Ears designation, which he called a "disaster."

"I've served under many presidents, seven to be exact," Hatch said. "But none is like the man we have in the White House we have today. When you talk this president listens."

Sen. Mike Lee's office disputed that the reductions were against the law. In an email, a spokesperson said they are "100% legal" and "well-supported by history." In an October speech, Lee also argued that past presidents have reduced national monuments by "hundreds of thousands of acres," as well as "by as much as 89% of the original reservation."

Rep. Chris Stewart, a Utah Republican whose district includes Grand Staircase-Escalante, said in a statement Monday that "I have seen firsthand the damage that the monument has caused to the local economy. My constituents have been in a desperate need of change, and today President Trump delivered."